CH. X] NITRATES. 253 



allowed to stand (preferably in vacuo over sulphuric acid), 

 characteristic crystals of copper oxide compound of amide 

 may be obtained. 



(2) A well-cooled mixture of potassium nitrite and 

 dilute sulphuric acid. 



Amides evolve nitrogen. 



(3) Boiling for some time with dilute acid. 

 Amides give ammonia in solution which can be tested 



for in the usual ways, best by heating with excess of mag- 

 nesia and testing for evolution of the gas. 



Ammonia, Nitrates, Nitrites, may be tested for 

 by ordinary methods in separate portions of the aqueous 

 solution. 



Ammonia, see DragendorfF, 97, p. 81. 



[ , see Fresenius, Qualitative Analysis, 10th ed. 

 Nitrites J 



pp. 228, 230. 



The most useful reagents for these substances are 

 metaphenylene-diamine and diphenylamine. Brucine in 

 strong sulphuric acid, and starch solution with zinc iodide 

 and acetic acid are also useful. 



If it is required to examine further the nature of the 

 proteids etc., this may be done by decomposing the 

 precipitates caused by addition of metallic salts. Precipi- 

 tates obtained from addition of copper, lead, and mercury 

 salts may be decomposed by H 2 S, those from sodium 

 phosphotungstate by excess of baryta (Ba(OH) 2 ) and sub- 

 sequent removal of excess of Ba(OH) 2 in filtrate by current 

 of CO* 



